Being the occasionally interesting ramblings of a major-league technophile.
Many people don't realize that in addition to making beer, Coors has long been a laboratory ceramics manufacturer. In 1958 this led to them taking a contract to produce pneumatic actuators and control systems designed to operate while glowing white hot. Though today this technology is used in places such as steel mills, originally it had a military application. A very deadly military application.
As the nuclear strike force began to shift emphasis from bombers to missiles in the late Fifties many options were evaluated. The biggest objection to ballistic missiles - at least in the minds of some planners - was that once you lit the fuse that was that. With bombers - before aerial refueling mainly the very long endurance B-36 - you could launch, move into a waiting position, and hold. Then return if the situation cooled.
One option explored to extend the wait time - as well as the range - was the nuclear powered bomber, which would have an endurance aloft similar to that of nuclear submarines below. However, exploration of the idea revealed some then - and in some cases still - insurmountable problems. Though one very heavily modified B-36 flew with a test reactor on board (it did not power the plane, which used its conventional engines) this option turned out to be infeasible. One of the biggest problems was that a crash would likely render the area for a good distance around the wreck uninhabitable. Another problem was that the weight of the shielding required to protect the crew created a major penalty to performance. So, what if there were no crew to protect, and what if there were enemy lands you wanted to render uninhabitable?
Drones were nothing new, even in the Fifties. Radio controlled aircraft had been around since the teens, with a few being experimented with for the Great War (WWI). Autonomous cruise missiles actually debuted in warfare with the V1 Buzz Bomb. Shielding a small package of electronics from a reactor would be much easier than protecting a human crew compartment. So, research began on an atomic-powered, long-range cruise missile.
Of course, as long as you're making the thing nuclear powered you might as well make it Nuclear Powered! Make it supersonic, at least in the final dash to target. Oh, and make it expendable, but not too expendable. There is a minimum size for a true reactor, which produces much more power than you need for just a cruise missile, even one with long range. So make the thing a delivery vehicle - an automated bomber - with nuclear submunitions it applies to multiple targets. Once those are expended, crash the delivery vehicle into an enemy facility.
To keep the weight low and improve reliability make the propulsion system as simple as possible. A ramjet (or athodyd) is about as simple as a heat engine can get. Cold air in + hot air out = thrust. The higher the temperature difference the better the thing works.
Ramjets aren't all that new, either. At least one ramjet powered plane flew in the late Thirties. Marquardt made chemical powered ramjets from the late Forties into the Sixties. They were used in a number of experimental vehicles, including the X-10 research drone. That vehicle was so successful Lockheed went on to make a target drone based on it. The only problem with that product was that it flew so high and fast it often outperformed the missiles used against it.
Hence the SLAM concept began evaluation and development. On January 1, 1957, the U.S. Air Force and the Atomic Energy Commission picked the Lawrence Livermore National Laboratory to do the job. SLAM stands for Supersonic Low-Altitude Missile. The vehicle was planned to use a half gigawatt reactor, with the undertaking to develop that being named Project Pluto. Later that name also came to refer to the overall project.
Building the reactor was a major project all by itself. Ramjets work better the more energy they can supply to the working medium (that is, air). That meant the hotter they could run the reactor, the better. Achieving the thrust required for the planned top speed meant running the reactor very hot. Hot enough to produce 513 Megawatts of thermal energy from an object the size of a large desk. So hot no metal would retain enough strength to resist the pressures from the flowing air hitting the front of it. The planners decided to use ceramics, instead. Coors was contracted to make the reactor fuel elements and the pneumatic control systems from advanced ceramics. Marquardt built everything in the engine except the reactor itself.
The reactor prototype was called TORY-IIA and ran for the first time in May 1961. TORY-IIA was a proof-of-concept power plant not intended for an actual flight-rated ramjet. Instead, it was run on the ground, just to test the design for power output and durability. It was followed by the larger and more powerful TORY-IIC. The latter was run-up on the ground to full power on 20 May 1964. The TORY-IIC consisted of 465,000 tightly packed small fuel rods of hexagonal cross-section, with about 27,000 channels between them for the high-pressure airflow. Normally, a ramjet needs to move through the air to force air into the inlet. For the ground tests, the airflow was provided by a huge reservoir of compressed air, made from an enormous length of drilling pipe. TORY-IIC produced a thrust of about 170,000 Newtons (38,000 lb) at a simulated airspeed of Mach 2.8. TORY-IIC was originally intended for use in the first flight tests, but operational missiles would probably have used a further improved model called TORY-III. The latter was still in the design phase when the whole program was cancelled.
The structure of this extraordinary craft was - of necessity - so rugged the vehicle was sometimes called "The flying crowbar." One project member liked to say the propulsion system was about as durable as a bucket of rocks.
As with the SR-71, entire new ways of making equipment resistant to the high operating temperatures had to be developed. As well, some old reliables from other uses were repurposed. After a number of exotic materials had been tried and found wanting as a coating for electric motor armatures, engineers found that exhaust manifold paint - obtained through an ad in Hot Rod magazine - worked perfectly.
Interestingly, the exhaust turned out to be not particularly radioactive. In fact, chemical poisoning from erosion in the exhaust of the beryllium oxide ceramic used would have been about as toxic as the radiation. Of course, the exhaust didn't need to be particularly dangerous, since the vehicle had an essentially unshielded half-Gigawatt reactor as the power source. The flight plan was to launch with solid rocket boosters to ramjet speed then start the reactor to climb and accelerate to cruise conditions. It would move to a Go/No Go position and wait to be sent into battle, or to the bottom of the deep ocean. If it did go on the attack, as SLAM approached the enemy's border it would dive to barely above treetop height to avoid radar, while flying to its targets at about Mach 3. The sonic boom alone would have pulped most living things under its path, while the radiation and heat from the reactor would sterilize everything.
Note the attack flight plan. Even after ballistic missiles came into service there was worry about anti-ballistic missile systems, while aircraft and standard cruise missiles would be vulnerable to the more conventional antiaircraft systems. SLAM would have been nearly impossible to intercept, even though it was the opposite of stealthy.
Despite what some have said and written about SLAM, it did not have infinite range. Within a couple of weeks the daughter products of the fission occurring in that hyperactive reactor would have begun reducing output. However, with a cruising range at 9000 meters of 182,000 kilometers and at 300 meters of 21,300 kilometers - at Mach 4.2 and 3.5 respectively - this thing could go anywhere on Earth in under six hours... and keep on going! It could be launched to a holding area, orbit there for a few days, then either bring armageddon or fly into the deepest part of the ocean.
Aerodynamically SLAM was effectively a lifting body, with tiny canard "wings" which were all-moving control surfaces, plus a Y tail. As planned, the vehicle was 26.8 meters long and 1.5 meters in diameter through the widest part of the body. The nose, leading edges and the body around the reactor would all have glowed bright orange during the attack phase, with the exhaust nozzle glowing yellow-white. The engine area and exhaust nozzle from the heat of the reactor, and the rest from air friction.
Pluto benefited from the nuclear rocket programs underway during roughly the same period, and they benefitted from it. Both required a very compact, very high-energy, very hot reactor. However, they still used different designs. One of the interesting things about the nuclear rockets which used hydrogen as a working medium (not as a fuel) was that under operating temperatures the graphite reactor moderator would combine with the working mass to produce methane. This would not only erode the core but lower performance by adding mass of a greater molecular weight than the hydrogen to the exhaust stream. Perhaps coating the graphite with the ceramic used by Pluto would avoided this problem.
Pluto/SLAM was cancelled on July 1, 1964, and even those working on it weren't really sad to see it go. However, many of the technologies live on. Besides the high-temperature ceramic pneumatic systems mentioned above, the project developed terrain following radar. This is today used for both manned aircraft and drones and cruise missiles.
There might actually be a use for the concept of a nuclear ramjet. The propulsion system can't be used in space, because it requires an atmosphere to work. However, that doesn't need to be our atmosphere. If we can make sure there's no life in the clouds of Venus or the gas giants we could use something similar to SLAM to explore them. Trust me, if you want to explore much of Jupiter, you need something fast just to get around Papa Jove in a reasonably timely manner.
I'll close with a bit of a digression. In what may be entirely coincidence, in 1958 the movie The Lost Missile debuted. The titular object was a huge, fusion powered rocket, protected from atmospheric heating by a magnetic sheath. In the movie it is discovered flying over the Arctic above a Soviet Bloc country. Unfortunately, the Soviets try to shoot it down, and cause it to begin flying around the Earth at an altitude of five miles. Researchers in the US speculate it is an alien craft, damaged by the Soviet attack and sent out of control. Between the sonic boom and the heat and ionizing radiation of the fusion drive, it is destroying everything it flies over. In just under an hour it will reach New York. If it isn't stopped, it will eventually fly over all the Earth. Was the ball-of-twine flight path planned from the beginning, or an accident? Is there even anyone left alive aboard after the attack?
One of the more laudable features of the story is that the rocket's origin is speculated, with no way to know for certain where it came from or what it was doing before being struck by that missile. There just isn't time for more in the desperate sequence of events.
The movie is told in near real time and except for one bizarre gaff is close to hard science fiction. That one gaff unfortunately not only involves someone saying that plutonium gives off "the most dangerous radiation known to man" but has that be an important plot point. Plutonium's natural radiation is primarily alpha particles, which can be stopped by a few inches of air or the layer of dead cells on the outside of the skin.
Aside from that - and a bit too much emphasis on a subplot involving one nuclear researcher trying to reach his pregnant wife in time for the birth of their child, plus a case of Stock Footage Syndrome of aircraft taking off and missiles launching - the move is recommended.
This document is Copyright 2015 Rodford Edmiston Smith. Anyone wishing to repost it must have permission from the author, who can be reached at: firstname.lastname@example.org